The invention is based on a method of adjusting the wavelength of lasers and a wavelength stabilization monitor for regulating the wavelength of a laser, comprising an optical input, a splitter, a wavelength filter in one branch, and two photodetectors.
Methods of wavelength stabilization and adjusting are known from the prior art, for example from U.S. Pat. No. 4,583,228. A wavelength monitor is used in this wavelength stabilization method. Here the light of a laser firstly passes through a beam splitter and strikes a photodetector in each of two branches. One of the two branches contains a Fabry-Perot interferometer. The photocurrents supplied by the two photodiodes are compared in a differential amplifier and supply a resultant error signal required for the control circuit. The wavelength monitor is set at a defined wavelength or group of wavelengths. For this purpose, in one optical branch the Fabry-Perot filter is tuned and in the other optical branch the reference level is set by purposive attenuation of the signal. This known prior art is also described in detail in FIGS. 1 to 3. However, this is an elaborate method and corresponding monitor. Tunable Fabry-Perot filters are mechanically sensitive and cannot be integrated in a module with suitably small structural dimensions.
Also the angle of incidence of the optical beam is a sensible figure. It is know from the U.S. Pat. No. 4,998,256 to rotate the etalon in front of the optical beam for a better adjustment of the central wavelength of the wavelength monitor. This kind of adjustment within a low tolerance margins is difficult to achieve in an industrial environment. Again this kind of solution is a high cost solution which shows no evidence for a small low cost product.
The advantage of the wavelength monitor and the method according to the invention is that it is easily possible to adapt the monitor to different wavelengths by moving building blocks comprising several components relative to each other. Here a wavelength filter is used which is not tunable and thus has reduced sensitivity in respect of mechanical problems. The method allows an optimal adaptation for a wavelength in a mounting process with an additional step of fixing the building blocks relative to each other.